从 Page1.xaml 导航到 Page2.xaml。 UWP xaml。 没有为此对象定义无参数构造函数。 Frame.Navigate 带参数

Question

Making a UWP app. Trying to navigate from Page1.xaml to Page2.xaml passing some parameters to Page2.xaml and I get the following error: No parameterless constructor defined for this object.

Page1.xaml has a for loop that adds buttons to navigate to Page2.xaml. Page2.xaml content is created dynamically and has different content depending on when button is clicked.

Example of buttons created: App 1 App 2 Game 1 Game 2

When you click on each button, different content is produced on Page2.xaml.

Code to add buttons on Page1.xaml with in the for loops is:

Button OpenAppButton = new Button();
OpenAppButton.Click += async delegate { Frame.Navigate(typeof(AppDisplay), AppDataTemp); };

AppDisplay is Page2.xaml. AppDataTemp is the parameters [string] being passed to Page2.xaml.

AppsDisplayStack.Children.Add(OpenAppButton);

The button is added to a StackPanel called AppDisplayStack.

Page2.xaml is the following code:

    <Grid>
        <StackPanel>
            <ScrollViewer>
                <StackPanel x:Name="AppStack" VerticalAlignment="Top" HorizontalAlignment="Center">
                </StackPanel>
            </ScrollViewer>
        </StackPanel>
    </Grid>

Everything else in Page2.xaml is created dynamically.

I have a feeling that I'm not passing the parameter correctly. If I try without parameters, Page2.xaml loads. Any ideas? Thanks in advance for any help.

Edit: Full error code: {System.MissingMethodException: No parameterless constructor defined for this object. at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean wrapExceptions, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor) at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean wrapExceptions, Boolean skipCheckThis, Boolean fillCache) at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, Boolean wrapExceptions) at System.Activator.CreateInstance(Type type, Boolean nonPublic, Boolean wrapExceptions) at Microsoft.UI.Xaml.Markup.XamlReflectionType.ActivateInstance() at Windows.UI.Xaml.Controls.Frame.Navigate(Type sourcePageType, Object parameter) at PermissionsAuditorViewer.AppsNGames.<>c__DisplayClass15_0.<b__0>d.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.b__7_0(Object state) at System.Threading.WinRTSynchronizationContextBase.Invoker.InvokeCore()}

Don't know if that helps.

UDPATE: Found the problem. I forgot that I changed the constructor for Page2.xaml from "public AppDisplay()" to "public AppDisplay(string URLData)". This was causing the issue. Thanks for the help guys. Appreicate it.

Answer 1

Would you be able to post more code or explain more? What is AppDataTemp and its type and are you pulling in e.Parameter or e.Parameter.YourModelsProperty on the other side of passing? If you are pulling from one page to another and binding its value to another instance of that object it will need to be the same type on both page's code-behind.

If your issue is No parameterless constructor defined for this object then it looks like you are not defining the frame correctly whether it be page 1 or page to (to or from), or you need to declare a variable of the same type to bind to whatever data you are passing with your navigation. From your explanation it sounds like you need to declare a model or your frame and will need something like

Frame rootFrame = this.Frame();

or

YourModel VarName = new YourModel(); on both pages or create an object on the page YourModel Varname { get; set; } YourModel Varname { get; set; } YourModel Varname { get; set; } on both pages and define it in your navigation function with VarName = e.Parameter;

or if you are passing in a simple bool, string, int, etc.

string VarName { get; set; } string VarName { get; set; } on both pages, and you can bind that to either VarName = e.Parameter or VarName = e.Parameter.YourModelStringProp

UPDATE: An example of using e.Parameter in your case would be something in your OnNavigated functions like:

YourModel VarName { get; set; }
string YourStr { get; set; }
protected override void OnNavigatedTo(NavigationEventArgs e){
    base.OnNavigatedTo(e);
    if (e.Parameter is string){  //common variable
        YourStr = e.Parameter;  //YourStr = e.Parameter.StrProp; //may need .ToString() for some
    }
    else //using a Model
    {
      YourModel = e.Parameter; // YourModel.YourProp = e.Parameter.YourProp;
    }
    //Use newly bound YourModel/YourStr here/elsewhere or call another function
    //function();
}

UPDATE 2: Would you be able to add more code with that error I believe it has something to do with your Navigation and declaring the Frame or declaring which Page you are Navigating too, if you post some code I may be able to see it easier. Im sure youre really close but I believe you forgot to declare your frame in OpenAppButton.Click += async delegate { Frame.Navigate(typeof(AppDisplay), AppDataTemp); }; OpenAppButton.Click += async delegate { Frame.Navigate(typeof(AppDisplay), AppDataTemp); }; and Im not sure how your layout is but you should be able to pull whatever you declared your Frame from in App.xaml.cs or create an instance on each page using something like

Frame rootFrame = Window.Current.Content as Frame;

then change that line to

OpenAppButton.Click += async delegate { rootFrame.Navigate(typeof(AppDisplay), AppDataTemp); };

If this doesnt help post some more code and I should be able to solve whats causing the issue.